The present invention relates to a blade for coating the surface of a sheet-like member or that of a cylindrical member with another substance or scraping off a substance from the surface of a member of the foregoing type.
Hitherto, doctor blades have been used in a variety of industrial fields. For example, the doctor blade has been used in a process for coating the surface of paper with resin or a process for coating the same with a heat sensitive material to manufacture heat sensitive paper, a process for coating the surface of sheet-like paper or another member with resin, a process for scraping off excess ink allowed to adhere to the surface of a printing plate and a process for molding rubber or foods into a sheet shape.
A major portion of the doctor blades has been made of a metal material, such as high-speed steel, and arranged in such a way that resin or the like is spread while the resin or the like is being pressed by the edge formed at the leading end of the doctor blade or ink or the like is scraped off. Doctor blades of a type made of a metal material however suffer from a problem in that inevitable wear of the edge of the doctor blade causes uniform coating to be impossible it leads to a fact that the doctor blade must be changed after it has been used for two hours, Thus there arises critical problems in that reliability and working efficiency are unsatisfactory.
To solve the above-mentioned problems, a method has been disclosed in Japanese Patent Publication No. 2-38671, in which a hard film made of tungsten carbide (WC) is thermally sprayed to the end surface of the blade. However, the foregoing blade can be used in only short time of about 80 hours because the hard film is separated during the operation.
Accordingly, a structure has been suggested in which, as disclosed in Japanese Patent Publication No. 2-51398, at least the cutting part of the blade is made of zirconia ceramics.
When the overall body of the doctor blade or the cutting part of the same is made of zirconia ceramics, the thickness must be considerably reduced to 1 mm or smaller. Therefore, if the doctor blade is deflected during the operation, there arises a risk that the doctor blade will be broken. If the blade is formed thick to prevent breakage, the blade cannot easily be deflected. In this case, there arise problems in that coating and scraping cannot easily be performed, thus resulting in that coating is performed nonuniformly and streaky defects take place.
In view of the foregoing, an object of the present invention is to provide a blade which cannot be broken when the blade is deflected during operation or handling and which exhibits excellent wear resistance.
A blade according to the present invention comprises a ceramic plate-like member having an edge and secured to the surface of at elongated metal plate in the leading end portion of the elongated metal plate, wherein the blade is deflected by 10 cm or more in the direction of the thickness thereof owning to the deadweight without breakage of the ceramic plate-like member when the blade is supported at two ends thereof which are apart from each other by 1 m or longer in the lengthwise direction thereof.
In order to satisfactorily perform an operation using the blade, the blade must appropriately be deflected. A variety of studies were performed by the inventor of the present invention. As a result, a preferred result can be obtained by adjusting materials, dimensions and shapes of the metal plate and the ceramic plate-like member and by making the blade to be deflected by 10 cm or more in the direction of the thickness of the blade owning to the deadweight when the blade is supported at two ends thereof which are apart from each other by 1 m or longer in the lengthwise direction thereof. Moreover, a structure in which the ceramic plate-like member is secured to the surface in the leading end portion of the metal plate enables the overall body of the blade to easily be deflected and the ceramic plate-like member to be protected from being broken when the blade is deflected.
A blade according to the present invention comprises a ceramic plate-like member having an edge and secured to the surface of an elongated metal plate in the leading end portion of the elongated metal plate, wherein the apparent Young's modulus E.sub.A (kg/cm.sup.2) of the overall body of the blade is defined as follows: EQU 1/E.sub.A =V.sub.1 /E.sub.1 +V.sub.2 /E.sub.2
when the Young's modulus of the ceramic plate-like member is E.sub.1 (kg/m.sup.2), the volume fraction of the same is V.sub.1, the Young's modulus of the metal plate is E.sub.2 (kg/m.sup.2) and the volume fraction of the sane is V.sub.2, and the following relationship is satisfied: EQU 5.times.10.sup.-10 &lt;A&lt;7.times.10.sup.-8
when the cross sectional secondary moment is I (m.sup.8), weight per unit length is W (kg/m) and A=5W/384E.sub.A I
That is, value A is a measure indicating the quantity of deflection realized by the deadweight of the blade. When the value A satisfies the above-mentioned range, the blade can be deflected.
A blade according to the present invention comprises a ceramic plate-like member having an edge and secured to the surface of an elongated metal plate in the leading end portion of the elongated metal plate, wherein the following relationship is satisfied: EQU E.sub.1 &lt;3.0.times.10.sup.10
when the fracture toughness level of the ceramic plate-like member is K.sub.C (kg/m.sup.3/2), the Vickers hardness of the same is H (kg/m.sup.2), and the Young's modulus of the same is E.sub.1 (kg/m.sup.2), and the following relationship is satisfied: EQU 2.00.times.10.sup.-8 &lt;R&lt;2.60.times.10.sup.-8
when R=(E.sub.1 /H).sup.4/5 /(K.sub.C.sup.1/2 +H.sup.5/8).
That is, the value R is the measure indicating the wear resistance. When the value R satisfies the above-mentioned range, the blade has satisfactory wear resistance and the same can appropriately be worn to be fitted to the shape of the coated surface.